KANSAS CITY, Mo. -- Attorneys for plaintiffs seeking a permanent injunction stopping the new concealed-guns law made those arguments Thursday in front of St. Louis Circuit Judge Steven Ohmer.

The hearing came 13 days after Ohmer granted a temporary injunction one day before the Missouri law was scheduled to take effect. Ohmer cited unresolved constitutional concerns that prompted Thursday's hearing.

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Is Jesse James At Fault For Gun Clause In State Constitution?

Some legal historians suggest a clause in the Missouri Constitution that appears to prohibit concealed guns came about because of Jesse James' crime spree in the late 19th century.

Jesse James was 28 years old when the constitution was drafted in 1875. State legislators were taking heat for James' crime spree, so a clause was included in the document to address those concerns, KMBC's Micheal Mahoney reported.

Article 1, Section 23 of the constitution reads: "That the right of every citizen to keep and bear arms in defense of his home, person and property, or when lawfully summoned in aid of the civil power, shall not be questioned; but this shall not justify the wearing of concealed weapons."

The clause has become the basis of the legal argument by opponents of the new law that allows most citizens in the state -- with proper certification and a background check -- to legally carry a concealed gun.

Attorney General Jay Nixon expects a direct appeal, by whichever side loses, to the Missouri Supreme Court.

Ohmer on Thursday granted a motion from the National Rifle Association to enter the case. "This is an important case. This court welcomes as much information as it can achieve," Ohmer said.

Burton Newman, a St. Louis attorney who is one of several lawyers representing plaintiffs in the case, said, "No party -- not even the NRA -- can claim that Missouri has a constitutional right to bear concealed arms."

But Nixon disagreed. His office, which is defending the law's constitutionality, has claimed that the questioned constitutional clause was a "reservation," not an absolute prohibition on lawmakers passing concealed-guns laws, which now exist in 44 states.

In a legal brief Monday, Nixon wrote "plaintiffs seek this unprecedented judicial intrusion armed with nothing more than a single, inapposite phrase from the Missouri Constitution. Having wholly failed to carry their burden," the lawsuit's claims "must fail," he argued.

"Missourians have enjoyed the constitutional right to bear arms for nearly two centuries, and Missouri courts have zealously protected that right," Nixon wrote.

Ohmer could rule on the permanent injunction as early as Friday.